Looking for some direction on building a 400 sbc. Im not exactly sure whats in the motor but i know its pretty close to stock. The guy i bought it from said it has an rv cam in it, but it has stock heads, an edelbrock performer intake, and an edelbrock 4 barrel carb. I have it hooked to a 2.38 gearbox. Give me some opinions on what to be shopping for to get the power i need. Not really looking for a go fast boat. I want some pep to it but I'm more focused on running dry and being able to have fun on it. Looking at new heads, new cam, and whatever else i may need to change to reach that goal. Thanks in advance

I have a buddy who is running a 383 and his engine has the Edelbrock heads, cam package. It runs very well and the price was fair for American made quality components.

Determine the rpm range you want to run and pick a cam that has a wide power curve. Then select a head CC to match your piston at a desired compression ratio. If wanting to run pump gas most engines would be limited to a 10:1 ratio on 91-93 octane.

If doing a full rebuild use someone with a reputation building airboat engines tat stay together

Avoid cheap heads with Chinese valves in them the valves don't last long before they burn up.

Lots of options for a sbc build so determine exactly what your needing to match gear and prop to engine.

Did he buy the top end kit? Ive looked at those before but saw some reviews saying the cam didnt match the heads to their best potential. Looking to rebuild mine with as little paid help as possible, but i know I'll potentially have to have some machining done to get my heads drilled for steam holes, etc.

It really depends on your budget, which sounds low, not knocking, just saying. The following assumes it is not installed and running it is not easy. I am also writing this from the standpoint of a minimum budget build, the most bang for the buck. Keep in mind, the go fast, have fun part is easy, the difficult goal cited is "Run Dry".

For starters, unless you know the history of the present build I revert to the history lessons I try to pass on whenever possible. A sure fire way of blowing up a rotating assembly is to slap a new set of heads on a worn out block, I have seen this happen so many times and the oil spill makes a hell of a mess. The first step is to try and determine the status of the present rotating assembly. Before doing anything, do a leak down test on the motor, you are looking for very consistent readings on all 8 cylinders. If you have any low cylinders, you need to determine if it is a ring or head issue. If leakage on the heads then fine (but that is an indication of some time on the motor), you are looking for any indications of issues with the block and rotating group.

Next, pull the heads, leaving the short block intact and mic the bores. Take it to a machine shop if needed for inspection. Are the bores round and consistent or worn, egg shaped and/or vary significantly over the stroke. Check the timing chain, is that good or worn out? A sloppy timing chain indicates a lot of time on the motor.

Assume the short block checks out, you now have something that is probably good up to maybe 5,000 RPM max (but probably better limited to 4,600), 9 or 10:1 compression and has potential to around 400 Hp. 9:1 is probably best on a used block, 10:1 being reserved for a short block rebuild. An RV cam is a good cam for this RPM range, if you can confirm what you have (pull timing cover and get P/N) you can confirm the specs.

Note that you mention a 2.38 gear box, let's call it 2,100 Prop RPM at 4,800 RPM. How big of a prop can you put on the boat? If you want to run dry, you should be thinking wide, 2 blade prop, probably about 78-80". There is more to be gained for the money in the prop than in the motor for sure.

What pistons are in it? Pull pan and look at underside, I'm pretty sure they are aftermarket. Are they dished, flat or doomed? Dished is good, flat probably works, doomed is a different story.

You can put money into aluminum heads if you want, but with no other changes, they are not going to add much power, the primary value is the weight savings. This is a cheapo build, the primary goal is building compression ratio (but don't forget my original advise, more pressure on worn bearings is a future blown motor). There are several head options, but the way to do it these days is a set of Vortec heads, they are smaller chamber and you gain the Vortec flow characteristics ideal for the RPM range. Another advantage is the knock resistance, the vortecs tolerate a bit of added compression ratio, 9:1 would need mid grade at most, premium gives more timing advance. $400 for a set of rebuilt Vortec heads and $300-$400 for an Edelbrock intake to match your carb and add the gaskets is about it, depending on the pistons presently installed. Drilling the steam holes just takes a drill press, but a machine shop can do for reasonable. My son actually has a set of used vortec heads with roller lifters and Edelbrock spread bore intake for sale, PM if interested.

So that's the low budget plan (other than the real low budget plan of just install). If you want more than 400 Hp, break out the wallet and build a 6,000+ RPM motor. I like the HotRod website as a good first cut on what is involved, but agree with Swamp about a reputable builder. But no way do you want to plan to turn an unknown rotating group beyond 5K, in particular an antique motor like the 400, those things are rare and have so much potential!

Slidin Gator, im swinging an 80 inch superwide whirlwind 2 blade as it is. Its a bit much for my motor in my opinion. Im running somewhere around 4700 rpms WOT and still don't run like i want it to. Anything over this rpm range i dont gain anything out of it except more wear on my motor. I mostly use my boat for fishing purposes, but I'd like to be able to do some of the rides that are relatively local. My budget isn't necessarily low, but its not a build im looking to do within a certain timeframe, either. I definitely don't want to turn my motor 6k+ rpms just because i know these motors are old and take a lot to build it to perform at that rpm. Just looking for some advice and direction on building it to perform how i want it to while still being reliable

glades cat wrote:Stud the block to clamp down the heads tight. The 400 has narrow deck surfaces between the bores. If you're running higher compression and turning it up, the heads have to be on there tight.

By the looks of your current build, with the prop and reduction, you need to spin that motor to about 5200 to 5300 to get what you want.
Looks like you need to change the cam ,heads and intake ,as far as cams go I've used the comp XM278H on several builds with good success ,eldebrock performer rpm heads (keep the intake runner in the 170 range for better torque),an rpm airgap manifold ,750 cfm carb
Just a few suggestions ,but will get you where you want to be performance wise.

Last edited by pax1ton on Fri Sep 28, 2018 10:24 pm, edited 1 time in total.

Supersteak217 wrote:Slidin Gator, im swinging an 80 inch superwide whirlwind 2 blade as it is. Its a bit much for my motor in my opinion. Im running somewhere around 4700 rpms WOT and still don't run like i want it to. Anything over this rpm range i dont gain anything out of it except more wear on my motor. I mostly use my boat for fishing purposes, but I'd like to be able to do some of the rides that are relatively local. My budget isn't necessarily low, but its not a build im looking to do within a certain timeframe, either. I definitely don't want to turn my motor 6k+ rpms just because i know these motors are old and take a lot to build it to perform at that rpm. Just looking for some advice and direction on building it to perform how i want it to while still being reliable

10-4 Supersteak, that helps a lot understanding the situation. As I said I was looking at the lowest budget option. If you are looking to dive into the rotating group and spend some money, then the feedback from everyone else is spot on, the RV cam does run out of steam below 5K RPM and your experience shows that.

Without more money on different gear and prop, aim for the 5,300-5,400 RPM range as stated above. I suggest an internal balance.

Talking reliability. Not feasible. She breaks then you have these new parts to start on the bottom end where you should be starting first. Not heads first, bottom end first. Doesn't matter the RPM you plan to turn. Bottom end first. What you got in a foundation??? No foundation no reliability. Are you currently running a 5.565" con rod that has a track record of breaking? Are you running dished hyper pistons? IMO, your current powerplant is a catastrophic failure just waiting to happen if you don't start on the bottom end first. Can be made reliable but not cost effective. JMO-

What you got???

IMO-
Scrap the idea of enhancing your current piece.

PM Glades Cat and ask him if he knows who builds a 23 degree 383 torque monster for a lot less money than you can reliably rebuild your 23 degree 400 SBC

IMHO, What is ur hp goal? A good 406 can make 560 to 600hp on pump gas. I would pull ur 400 down and inspect the deck for cracks between steam holes and bolt holes.If block is good, Re use ur factory crank, put in 5.7" or 6.0" rods with a matching piston for 10 to 1 compression, no more than 10.5 to 1. I would use no smaller than a 210cc aluminum head and 220 or 227 would be better with a 2.10 intake valve. A Huricane intake port matched to ur heads. A roller cam with about .630 lift on a smallish duration. A 1050 4150 style carb and you would be nock in on 600hps door. All very tame for an everyday boat. I have built quite a few of these exact engines in 1970s blocks with 11.5 to1 comp and ran high 9s in 1/4 mile. The 400 cranks are very good for what they are. I have spun them 8200rpm continuously without any problems. Internal balance the rotating assembly. Scat I beam rods are my first choice (they are light) and balance good with the crank. Pick your heads first,(they determine how much power you can make) then the cam that will allow the head to reach max flow, and build the block to them with the appropriate piston. If you purchase the parts, have the block work done and assemble yourself budget would be around $5000 to $7000. Have it built at a shop probably $8500. Or you could buy a LS3, change the cam an springs with a retune and have 580hp.

A buddy has a 400 solid lifter motor in his buggy and he is tired of dealing with it. Way too much fuel and every time he puts his foot down it something in his toyota running gear breaks, wrong combo. He likes the 6 gallons all day the rest of us are getting out of the 6 cylinders. Interested in a 4.3 running motor for running motor swap.